In general, a fuel cell system includes a fuel cell which generates electric power by chemically reacting fuel gas and oxidizing gas, and a cooling water path for cooling the fuel cell which generates heat resulting from the power generation, and is configured to control the temperature of the fuel cell by regulating the rate (degree) of cooling according to a power generation amount.
If the fuel cell system having the above configuration is left outdoors without being operated for a certain time or longer, water within the cooling water path freezes as an outside air temperature decreases. As a result of this, power generation might be unfeasible because of a failure to perform temperature control of the fuel cell at next start-up, etc.
In view of the circumstance, for example, there is known a fuel cell system which includes an outside air temperature detecting means for directly or indirectly detecting an outside air temperature and a water temperature detecting means for detecting the water temperature of cooling water, and executes a freezing suppressing operation based on the outside air temperature detected by the outside air temperature detecting means and the water temperature detected by the water temperature detecting means (e.g., Patent Literature 1).
FIG. 15 is a block diagram showing a configuration of a conventional fuel cell system disclosed in Patent Literature 1.
As shown in FIG. 15, the conventional fuel cell system includes a fuel cell 36 for generating electric power using fuel gas and oxidizing gas, a cooling water path 37 through which cooling water for cooling the fuel cell 36 flows, a hot water path 38 through which hot water which recovers heat from the cooling water flowing through the cooling water path 37 flows, a hot water storage tank 39 for storing hot water generated by recovering heat from the cooling water, a heat exchanger 40 for exchanging heat between the cooling water in the cooling water path 37 and the hot water in the hot water path 38, a cooling water circulator 41 for circulating water in the cooling water path 37, a heater 42 for heating the cooling water path 37, a hot water circulator 43 for circulating the water in the hot water path 38, an outside air temperature detecting means 44 for detecting an outside air temperature, a cooling water temperature detecting means 45 for detecting the temperature of the cooling water, a hot water temperature detecting means 46 for detecting the temperature of the hot water, and a controller 47.
When the controller 47 determines that the water in the cooling water path 37 and the water in the hot water path 38 will possibly freeze based on the outside air temperature detected by the outside air temperature detecting means 44, the cooling water temperature detected by the cooling water temperature detecting means 45 and the hot water temperature detected by the hot water temperature detecting means 46, it causes the cooling water circulator 41 to circulate the cooling water, the hot water circulator 43 to circulate the hot water, and the heater 42 to perform heating, as the freezing suppressing operation. This can suppress the cooling water and the hot water from freezing.
When the fuel cell system is abnormally shut down for some cause or another, the controller 47 determines whether or not each of the cooling water path 37 and the hot water path 38 should execute the freezing suppressing operation based on the cause.
For example, in a case where the fuel cell system is abnormally shut down due to leakage of water from the cooling water path 37, the cooling water circulator 41 operates without the cooling water if the cooling water circulator 41 circulates the cooling water as the freezing suppressing operation, and therefore the controller 47 does not execute circulating of the cooling water. In this case, if the heater 42 performs heating as the freezing suppressing operation, it performs heating in a state in which there is no cooling water to be heated in the cooling water path 37, and therefore a region in the vicinity of the heater 42 is more likely to be heated in excess. For this reason, the controller 47 causes the heater 42 not to perform heating. For example, in a case where the fuel cell system is abnormally shut down due to leakage of water from the hot water path 38, the hot water circulator 43 operates without the hot water if the hot water circulator 43 circulates the hot water, and therefore the controller 47 does not execute circulating of the hot water. In this way, damage to the cooling water circulator 41, the hot water circulator 43 and the heater 42 which are components for executing the freezing suppressing operation is suppressed.
The leakage of water from the cooling water path 37 is detected as follows, for example.
If water leaks from the cooling water path 37 during power generation of the fuel cell 36, the temperature of the fuel cell 36 increases excessively. Therefore, by detecting the excessive increase in the temperature of the fuel cell 36, the leakage of water from the cooling water path 37 can be detected. In a case where the fuel cell system includes as the cooling water temperature detecting means 45, a first cooling water temperature detecting means 48 for detecting the water temperature of cooling water at an inlet side of the fuel cell 36 and a second cooling water temperature detecting means 49 for detecting the water temperature of cooling water at an outlet side of the fuel cell 36, a heat exchange ability of the heat exchanger 40 decreases if water leaks from the hot water path 38 during the power generation of the fuel cell 36, so that the cooling water temperature detected by the first cooling water temperature detecting means 48 gets close to the cooling water temperature detected by the second cooling water temperature detecting means 49. Therefore, by detecting the fact that the cooling water temperature detected by the first cooling water temperature detecting means 48 is close to the cooling water temperature detected by the second cooling water temperature detecting means 49, leakage of water from the hot water path 38 can be detected.